As a method for releasing a molding product including an optical element which is a product portion from a molding die, a method in which an ejector pin or a core portion for forming the product portion, added to the die, is pushed out toward an opposing die side and the product portion is released with a gate portion and a runner portion, attached to this product portion, is known (refer to, for example, Patent Literature 1).
In the method of Patent Literature 1, when the product portion is minute, it is difficult to ensure a space in which the ejector pin is provided. In addition, also the configuration in which the core portion forming the product portion is pushed out has limitation in reducing a thickness or a size of the core portion in accordance with the product portion, and machining is difficult. Furthermore, even if such a core portion can be machined, rigidity of the core portion cannot be ensured, and molding with good reproducibility while the product portion is pushed out is difficult.
Moreover, there is also a method in which a projection portion formed on a flange part other than an optical surface or on a flange portion opposite to a gate portion in the optical element which is the product portion is pushed out (refer to, for example, Patent Literature 2).
In the method of Patent Literature 2, when the product portion is minute, the flange portion is also minute, and provision of the protruding portion is difficult. In addition, when the protruding portion is to be provided on the side opposite to the gate portion, in the minute product portion, after a resin is filled in the projection portion, the resin is instantaneously cooled and solidified, whereby formation of the projection portion is made difficult.
Note that there is considered a method in which the product portion is not pushed out but only the runner portion is pushed out. However, a stress is applied to the gate portion attached to the product portion at the time of pushing-out, and it is likely that bending or rupture occurs.
Furthermore, from a different point of view, in order to relax the stress applied to the gate portion of the molding product, there can be considered a method in which a thickness of the flange portion and a thickness of the gate portion are made equal, and molding surfaces for forming the flange portion and the gate portion are made flush with each other (refer to, for example, Patent Literature 1). Moreover, a shape of the gate portion is also considered to be devised so as to be suitable for releasing. For example, the shape of the gate portion can be smoothly connected from an outer side of a lens which is the product portion to the runner portion (refer to, for example, Patent Literature 3).
With the shape of the gate portion in Patent Literature 1, rigidity of the gate portion can be ensured by making the thickness of the gate portion and the thickness of the flange portion equal to each other. In addition, by making the molding surfaces of the flange portion and the gate portion, on a fixed die side, flush with each other, there is no notch (cutout) shape which might result in occurrence of a crack (split) at the time of releasing. However, in the case of the minute product portion, in the configuration in which there is no pushing-out mechanism for the product portion and the runner portion in front of the gate portion is pushed out in a direction perpendicular to a parting surface, a portion where the gate thickness begins to change in order to connect the gate portion to the runner portion is bent. As a result, there is a risk that a crack occurs in the gate portion, the gate portion is ruptured, and taking-out of the product portion becomes difficult.
With the shape of the gate portion in Patent Literature 3, the shape of the gate portion becomes wide with respect to the product portion, and gate cutting along the outer shape of the product portion becomes difficult. Namely, even if the gate cutting is performed, a part of the gate portion remains largely in many cases, and when the product portion is to be assembled to a holder or the like, restriction on a recess shape of the gate portion on the holder side becomes large.
In addition, when the molding product is pushed out, there is a method in which the product portion is pushed out in the direction perpendicular to the parting surface, and the runner portion is pushed out in a direction diagonal to the direction perpendicular to the parting surface (refer to patent Literature 4, for example). In the method of Patent Literature 4, the runner portion is pushed out along the gate portion formed by inclination to thereby cut off the product portion and the gate portion.
In the minute product portion, when a mold surface is deep, and an outer circumferential side surface of the product portion is perpendicular or substantially perpendicular to a mold mating surface, even if the runner portion is pushed out in the diagonal direction without providing a mechanism for pushing out the product portion, there is a risk that an outer circumferential portion of the product portion is caught by the die, and bending and rupture occur in the gate portion.